Investigated Composition Range Research Articles

Spin-glasslike behavior in rhombohedral (Ge,Mn)Te–(Sn,Mn)Te mixed crystal

We present studies of magnetic and transport properties of Ge1−x−ySnxMnyTe mixed crystals with chemical compositions 0.083≤x≤0.142 and 0.012≤y≤0.119. The transport characterization measurements were performed at temperatures 4.2<T<300 K. The results showed feature characteristic for narrow gap semiconductors, e.g., metallic conductivity with ρxx≈10−4 Ω cm and hole concentrations p>1021 cm−3. It was found that the transport properties strongly depend on the chemical composition of the alloy. The magnetic investigations included measurements of linear χ1 and harmonic χ2,3 ac susceptibilities as a function of temperature and of the applied magnetic field amplitude and frequency. Qualitative analysis of our experimental data showed that in the studied system, in the investigated composition range, the spin glass order exists at temperatures up to 50 K.

Kinetics of Se 75S 25− xCd x glassy system using differential scanning calorimeter

The kinetics of crystallization in Se 75S 25− x Cd x ( x = 0, 2, 4, 6 and 8) chalcogenide glasses are studied by non-isothermal methods using differential scanning calorimetery at different heating rates of 5, 10, 15 and 20 K/min. The growth kinetics has been investigated using Kissinger, Matusita and Ozawa models. The values of glass transition temperature ( T g), and crystallization temperatures ( T c) are found to be composition and heating rate dependence. From the heating rate dependence of T g and T c, the activation energy for structural relaxation (Δ E t), the activation energy of crystallization (Δ E c), crystallization enthalpy (Δ H c) and the order parameter ( n) are calculated. It was observed that the glass transition temperature and crystallization temperatures both increase with increasing heating rates. It was observed that Se 75S 25 has a minimum value of activation energy of structural relaxation, which indicates that this particular glass has a larger probability to jump to a state of lower configurational energy and higher stability in the glassy region. On the basis of the obtained experimental data the temperature difference ( T c − T g) and the enthalpy released are found to be minimum and maximum, respectively for Se 75S 21Cd 4 glass, which indicates that this glass is the least stable glass in the composition range of investigation.

Optical properties and structural characteristics of ZnMgO grown by plasma assisted molecular beam epitaxy

Wurtzite Zn1−xMgxO thin films with Mg contents between x=0 and x=0.37 were grown on c-plane sapphire substrates by plasma assisted molecular beam epitaxy using a MgO/ZnMgO buffer layer. The a-lattice parameter is independent from the Mg concentration, whereas the c-lattice parameter decreases from 5.20 Å for x=0 to 5.17 Å for x=0.37, indicating pseudomorphic growth. The near band edge photoluminescence shows a blueshift with increasing Mg concentration to an emission energy of 4.11 eV for x=0.37. Simultaneously, the energetic position of the deep defect luminescence shows a linear shift from 2.2 to 2.8 eV. Low temperature transmission measurements reveal strong excitonic features for the investigated composition range and alloy broadening effects for higher Mg contents. The Stokes shift as well as the Urbach energy is increased to values of up to 125 and 54 meV for x=0.37, respectively, indicating exciton localization due to alloy fluctuations.

The effect of salt on the association between linear cationic polyelectrolytes and sodium dodecyl sulfate

The aggregation of polyelectrolyte–surfactant particles has been investigated at large excess of the surfactant in the presence of NaCl using coagulation kinetics, electrophoretic mobility and dynamic light scattering measurements. The investigated systems were mixtures of sodium dodecyl sulfate (SDS) with poly(vinylamine) (PVAm) as well as with poly(diallyldimethylammonium chloride) (PDAC). The observed variation of the initial rate of coagulation with NaCl concentration of PVAm–SDS and PDAC–SDS particles is in qualitative agreement with the predictions of DLVO theory. This finding provides evidence for the formation of electrostatically stabilized colloid dispersions in the investigated composition range of these mixtures. The kinetic stability of these dispersions increases with increasing SDS concentration and polyelectrolyte charge. The colloid dispersion nature of polyelectrolyte–surfactant mixtures has important consequences with respect to the surface and phase behaviour of these systems in the presence of supporting electrolyte.

Calorimetric studies of the crystallization process in a-Se 75S 25−xAg x chalcogenide glasses

Calorimetric studies of amorphous Se 75S 25− x Ag x ( x = 2, 4, 6 and 8) chalcogenide glasses are made at different heating rates (5, 10, 15 and 20 K/min) under non-isothermal condition using Differential scanning calorimetry. The values of glass transition temperature and crystallization temperature are observed to be composition and heating rate dependence. From the heating rate dependence of glass transition temperature and crystallization temperature, the activation energy for structural relaxation (Δ E t), the activation energy of crystallization (Δ E c) and the order parameter ( n) have been calculated. It is observed that Se 75S 19Ag 6 has a minimum value of activation energy for structural relaxation (Δ E t), which indicates that this particular glass has a larger probability to jump to a state of lower configurational energy and higher stability in the glassy region. On the basis of the obtained experimental data the temperature difference ( T c − T g) is found to be maximum for Se 75S 19Ag 6, which further indicate that this glass is the thermally most stable in the entire composition range of investigation.

A conductivity study and calorimetric analysis of dried poly(sodium 4-styrene sulfonate)/poly(diallyldimethylammonium chloride) polyelectrolyte complexes

Ionically cross-linked polyelectrolyte complexes (PECs) of anionic poly(sodium 4-styrene sulfonate) (PSS) and cationic poly(diallyldimethylammonium chloride) (PDADMAC), xPSS.(1-x)PDADMAC, with molar fractions x ranging from 0.30 to 0.70, were prepared and subsequently dried. The PEC samples were analyzed by differential scanning calorimetry, and the ionic conductivity sigmadc of the samples was measured as a function of temperature by means of impedance spectroscopy. The thermograms display an endothermic peak in the temperature range of 90-143 degrees C, which is attributed to a glass transition of the PEC. The glass transition temperature Tg has a symmetric x dependence with a minimum at x=0.50. The temperature dependence of sigmadcT is not affected by the glass transition. The ionic conductivity of the samples before drying is three orders of magnitude larger than sigmadc after drying; nevertheless, their activation enthalpies are identical. Arrhenius parameters obtained from the systematic study of several PEC compositions are discussed. The ionic conductivity of the PSS-rich samples is significantly higher than sigmadc of PDADMAC-rich samples. This implies a relatively high Na+ mobility as compared to Cl(-) mobility in PEC. In contrast to the symmetric x dependence of Tg, the conductivity of PEC increases and the activation enthalpy decreases with increasing x in the investigated composition range. A strong x dependence of sigmadc is observed for PSS-rich PEC, which is attributed to a significant variation in the mobility of the charge carriers.

The Fe–Ni–Al phase diagram in the Al-rich (>50 at.% Al) corner

The ternary Fe–Ni–Al phase diagram between 50 and 100 at.% Al was investigated by a combination of powder X-ray diffraction (XRD), differential thermal analysis (DTA) and electron probe microanalysis (EPMA). Ternary phase equilibria and accurate phase compositions of the respective equilibrium phases were determined within the isothermal section at 850 °C. The crystal structure of τ1 (Fe 4− x Ni x Al 10) and τ2 (Fe 2− x Ni x Al 9) was determined by means of single crystal X-ray diffraction. The decagonal quasi-crystalline phase q (Fe 4.9Ni 23.4Al 71.7) was found to be stable between 850 °C and 930 °C. All experimental data were combined to yield a ternary reaction scheme (Scheil diagram) involving 10 ternary invariant reactions in the investigated composition range, and a liquidus surface projection was constructed based on DTA results.

Thermochemical study of trivalent-doped ceria systems: CeO2–MO1.5(M = La, Gd, and Y)

The formation enthalpies from the oxide end-members (ΔHf,ox) of the CeO2–MO1.5(M = La, Gd, and Y) systems were determined by high temperature oxide melt drop solution calorimetry. In each system, ΔHf,oxis slightly positive over the investigated composition range with a maximum at a certain doping level. Above that concentration, ΔHf,oxdecreases rapidly and stays almost constant. Such behavior is strikingly different from the strongly negative ΔHf,oxof the ZrO2–YO1.5and HfO2–YO1.5systems. The absence of substantial energetic stabilization in the CeO2–MO1.5systems may be attributed to the large size of Ce4+, which has no preference for 7-coordination like the smaller Zr4+or Hf4+ions. The primary defect associates in CeO2–MO1.5are proposed to be neutral trimers with oxygen vacancies nearest neighbor to the dopant cations. It is also suggested that the maximum ΔHf,ox(destabilization) of CeO2–MO1.5is determined by the local site distortion rather than the global lattice deformation. The relatively stable region after the maximum ΔHf,oxmay be attributed to the somewhat stabilizing long-range defect–defect interactions, which become effective above a certain doping level.

The In–Pt–Sb phase diagram

Abstract The ternary phase diagram In–Pt–Sb was studied in two isothermal sections at 400°C and 700°C, respectively, using X-ray powder diffraction (XRD), electron-probe microanalysis (EPMA), and metallographic techniques. The ternary phase reactions were determined by differential thermal analysis (DTA) in the composition range between 0 and 50at.% Pt. The obtained experimental phase diagram data were combined with literature data on the limiting binary systems to construct a ternary reaction scheme (Scheil diagram) in the investigated composition range between 0 and 50at.% Pt. The liquidus surface was derived from the results of DTA measurements.

Differential scanning calorimetric study of Se 80Te 20−xCu x chalcogenide glasses

Results of differential scanning calorimetric (DSC) under non-isothermal condition of bulk amorphous semiconducting alloys of Se 80Te 20− x Cu x ( x=2, 4, 6, 8 and 10) glasses with different heating rates are reported and discussed. The glass transition temperature, crystallization temperature at different heating rates and structural change during glass transition have been determined from an empirical relation. The dependence of the glass transition temperature ( T g), crystallization temperature ( T c), the activation energy for structural relaxation (Δ E t), the activation energy of crystallization (Δ E c) and the order parameter ( n) are calculated at different heating rates. On the basis of the obtained experimental data, the temperature difference T c− T g is found to be maximum for Se 80Te 16Cu 4 glass, which indicates that this glass is the thermally most stable in the composition range of investigation.

Preparation of poly(vinyl alcohol)–silicone based hybrid membranes for the pervaporation separation of water–acetic acid mixtures

Hybrid membranes were prepared using poly(vinyl alcohol) (PVA) and tetraethylorthosilicate (TEOS) via hydrolysis followed by condensation. The obtained membranes were characterized by Fourier transform infrared spectroscopy, wide-angle x-ray diffraction and differential scanning calorimetry. A remarkable decrease in degree of swelling was observed with increasing TEOS content in membranes and is attributed to the formation of hydrogen bonding and covalent bonds in the membrane matrix. The pervaporation performance of these membranes for the separation of water–acetic acid mixtures was investigated in terms of feed concentration and the content of TEOS used as cross-linking agent. The membrane containing 1 : 2 mass ratio of PVA and TEOS gave the highest separation selectivity of 1116 with a flux of 3.33 × 10−2kg/m2h at 30°C for 10 mass% of water in the feed. Except for membrane M-1, the observed values of water flux are close to the values of total flux in the investigated composition range, signifying that the developed membranes are highly water selective. From the temperature dependence of diffusion and permeation values, the Arrhenius apparent activation parameters have been estimated. The resulting activation energy values obtained, showing that water permeation is lower than that of acetic acid, suggest that the membranes have higher separation efficiency. The activation energy values calculated for total permeation and water permeation are close to each other for all the membranes except membrane M-1, signifying that coupled-transport is minimal because of the higher selective nature of membranes. The negative heat of sorption values (ΔH s) for water in all the membranes suggests a Langmuir mode of sorption.

Pervaporation separation of water–acetic acid mixtures through poly(vinyl alcohol)-silicone based hybrid membranes

Hybrid membranes were prepared using poly(vinyl alcohol) (PVA) and tetraethylorthosilicate (TEOS) via hydrolysis followed by condensation. The obtained membranes were characterized by Fourier transform infrared spectroscopy, wide-angle X-ray diffraction and differential scanning calorimetry. The remarkable decrease in degree of swelling was observed with increasing TEOS content in membranes and is attributed to the formation of hydrogen and covalent bonds in the membrane matrix. The pervaporation performance of these membranes for the separation of water–acetic acid mixtures was investigated in terms of feed concentration and the content of TEOS used as crosslinking agent. The membrane containing 1:2 mass ratio of PVA and TEOS gave the highest separation selectivity of 1116 with a flux of 3.33 × 10 −2 kg/m 2 h at 30 °C for 10 mass% of water in the feed. Except for membrane M-1, the observed values of water flux are close to the values of total flux in the investigated composition range, signifying that the developed membranes are highly water selective. From the temperature dependence of diffusion and permeation values, the Arrhenius apparent activation parameters have been estimated. The resulting activation energy values, obtained for water permeation being lower than those of acetic acid permeation values, suggest that the membranes have higher separation efficiency. The activation energy values calculated for total permeation and water permeation are close to each other for all the membranes except membrane M-1, signifying that coupled-transport is minimal as due to higher selective nature of membranes. Further, the activation energy values for permeation of water and diffusion of water are almost equivalent, suggesting that both diffusion and permeation contribute almost equally to the pervaporation process. The negative heat of sorption values (Δ H s) for water in all the membranes suggests the Langmuir's mode of sorption.

The Al–Ni–Si phase diagram. Part II: phase equilibria between 33.3 and 66.7 at.% Ni

The ternary Al–Ni–Si phase diagram between 33.3 at.% Ni and 66.7 at.% was investigated by a combination of differential thermal analysis (DTA), powder X-ray diffraction (XRD), metallography and electron probe microanalysis (EPMA). Ternary phase equilibria were investigated within three isothermal sections at 550, 800 and 1000 °C and the homogeneity ranges at these temperatures were determined by means of EPMA. Powder XRD was used to investigate the variation of lattice parameters with the composition for the different solid solution phases, in particular the solid solutions of Si in AlNi and of Al in δ-Ni 2Si. DTA was used to identify a total number of 13 invariant ternary reactions yielding a complete description of ternary equilibrium reactions in this part of the phase diagram. A liquidus projection of the entire investigated composition range was constructed by combining our own DTA data with literature data for the limiting binary systems. The binary Ni–Si phase diagram was reinvestigated within the composition area of the high temperature phase θ-Ni 2Si by means of DTA. Based on our experimental results we propose to regard ternary Al ySi 9−yNi 13±x (τ 4) and binary θ-Ni 2Si as one single solid solution phase.

Phase selection in undercooled Fe–Nd alloy melts

Abstract Undercooling experiments on Fe89.5Nd10.5, Fe87.5Nd12.5 and Fe75Nd25 alloy melts have been performed by electromagnetic levitation and drop tube experiments. Phase formation in Fe–Nd alloys is of interest due to the ternary compound Fe14Nd2B1, which exhibits extraordinary hard magnetic properties. Under equilibrium solidification conditions, melts of the investigated composition range solidify primarily in the γ-Fe solid solution, which is followed by the peritectic formation of the chemically ordered Fe17Nd2-phase. In electromagnetic levitated Fe75Nd25 alloys the primary crystallisation of γ-Fe could be suppressed in favour of the peritectic phase with rising undercooling. In Fe-rich alloys the direct crystallisation of the Fe17Nd2-phase was only observed in drop tube solidified particles with diameters below 0.2 mm.

Electrical transport and magnetotransport studies in WEAK ITINERANT amorphousFe90−xMnxZr10(0<~x<~16)alloys

Zero-field and in field electrical resistivity, magnetoresistivity, and magnetization measurements have been performed in the temperature range of 4.2 K to 300 K and in the fields up to 60 kOe on amorphous ${\mathrm{Fe}}_{90\ensuremath{-}x}{\mathrm{Mn}}_{x}{\mathrm{Zr}}_{10}(0l~xl~16)$ alloys. Unusual properties such as a broad resistivity minimum in the higher-temperature region and a resistivity minimum close to Curie temperature were observed for alloys with a certain Mn content. An analysis of the resistivity data using existing theories reveals the actual functional dependencies of resistivity on temperature in different temperature ranges. The enhancement of spin fluctuation with Mn concentration has been observed from resistivity data and is further supported by the magnetization data. A comparative study of magnetic and transport properties indicates that remarkable effects due to magnetic ordering are present in both resistivity and magnetoresistivity. The observed composition dependence of the spontaneous resistive anisotropy is explained in terms of the two-current-conduction model. The determined values of composition dependence of spin-up and spin-down residual resistivity provide conclusive evidence of weak itinerant ferromagnetism over the entire composition range of the present investigation. These results are further supported by the high-field dc susceptibility data obtained from magnetization measurements.

Experimental determination of the activity of chromite in multicomponent spinels

We determined activity–composition relationships in Pt-Cr and Pt-Fe-Cr alloys at 1300°C experimentally and used the results to constrain the thermodynamic properties of chromite–picrochromite spinels. The Pt-Cr binary is characterized by strong negative deviations from ideality throughout the investigated composition range and the activity–composition relationship can be fit by a four-suffix asymmetric regular solution with three binary interaction parameters. The ternary alloy was modeled as a four-suffix asymmetric regular solution; the three ternary interaction parameters in this model were constrained by combining interaction parameters for the three bounding binaries taken from this and previous work with results for a set of experiments in which the activity of Cr in Pt-Fe-Cr-alloys was fixed by coexisting Cr 2O 3 at known f O 2. The free energy of formation of FeCr 2O 4 at 1300°C was determined using the activities of Fe and Cr in Pt-alloys in equilibrium with oxide mixes of FeCr 2O 4 and Cr 2O 3. The free energy of formation of chromite from Fe+Cr 2O 3+O 2 is −202.7 ± 0.4 kJ/mol (1σ), indistinguishable from literature values. The corresponding free energy of formation of FeCr 2O 4 from the elements is −923.5 ± 2.1 kJ/mol (1σ), and the enthalpy of formation at 298 K is −1438 kJ/mol. The activity–composition relationship for the chromite component in (Fe,Mg)Cr 2O 4 solid solutions was determined from a set of experiments in which Pt-alloys were equilibrated with spinel + Cr 2O 3. (Fe,Mg)Cr 2O 4 spinels are nearly ideal at 1300°C; modeling our data with a one-site symmetric regular solution yields an interaction parameter of +2.14 ± 0.62 kJ/mol (1σ), similar to values based on data from the literature.

Oxygen diffusion in the ceramic composite of YBa 2Cu 3O y with Y 2BaCuO 5

The influence of secondary Y211 phase on the oxygen diffusion in the ceramic composite of Y123 with Y211 addition has been investigated by the isothermal electric resistance relaxation. The activation energy of oxygen diffusion in the Y123 matrix of the composite is obtained as 1.13, 1.04 and 0.97 eV for the composite of Y123 with x mol Y211, x=0, 0.2, 0.4 respectively, i.e., it is decreased with the Y211 addition in the investigated composition range.

The Al–Ni–Si phase diagram between 0 and 33.3 at.% Ni

The ternary Al–Ni–Si phase diagram between 0 and 33.3 at.% Ni was investigated by a combination of differential thermal analysis (DTA), powder X-ray diffraction (XRD), metallography and electron probe microanalysis (EPMA). Ternary phase equilibria and accurate phase compositions of the respective equilibrium phases were determined within the isothermal section at 550 °C by means of EPMA. Al 3Ni 2 and NiSi 2 were found to form extended ternary solid solutions while Al 3Ni and the ternary phase Al 6Ni 3Si have only small homogeneity ranges within the ternary system. The variation of lattice parameters with the composition was studied for all solid solution phases. DTA was used to investigate ternary phase reactions. A total number of five invariant reactions could be derived from DTA data, i.e. one ternary eutectic reaction, three transition reactions and one ternary peritectic reaction. All experimental data were combined to yield a ternary reaction scheme (Scheil diagram) of the investigated composition range and a liquidus surface projection was constructed based on DTA results. The melting behavior of the extended solid solution phase NiSi 2− x Al x was studied in detail by DTA measurements at low heating rates. The melting reaction was found to change from peritectic decomposition in the binary Ni–Si system to congruent melting at approximately 20 at.% Al.

Simultaneous measurements of thermal conductivity and diffusivity of Se80Te20-xInx (x = 2, 4, 6 and 10) chalcogenide glasses at room temperature

Measurements of thermal conductivity and thermal diffusivity of twin pellets of Se80Te20-xInx (x = 2, 4, 6 and 10) glasses, prepared under a load of 5 tons were carried out at room temperature using transient plane source (TPS) technique. The measured values of both thermal conductivity and diffusivity were used to determine the specific heat per unit volume of the said materials in the composition range of investigation. Results indicated that both the values of thermal conductivity and thermal diffusivity increased with the addition of indium at the cost of tellurium whereas the specific heat remained almost constant. This compositional dependence behaviour of the thermal conductivity and diffusivity has been explained in terms of the iono-covalent type of bond which In makes with Se as it is incorporated in the Se-Te glass.

THE LOCAL STRUCTURE OF BISMUTH-BORATES CHARACTERIZED BY 11B MAS NMR

Bismuth-borate glasses and vitroceramics belonging to x Bi 2 O 3 · (100 - x) B 2 O 3 system, 0 ≤ x ≤ 93, doped with 0.5 mol% MnO are investigated by 11 B Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR). The 11 B MAS NMR results indicate the presence of three- and tetra-coordinated boron in all investigated bismuth borates. While the fraction of the tetra-coordinated boron present a large maximum in the range 20 ≤ x ≤ 60 in the bismuth-borate glasses, this maximum is reduced to the range 20 ≤ x ≤ 37.5 in the samples obtained after heat treatment. Crystalline phases are developed in the samples with high bismuth content, x ≥ 60, by heat treatment at 550°C, in which two types of three-coordinated boron are identified. The mean values of the NMR parameters like chemical shift, asymmetry parameter and quadrupolar coupling constant are less influenced by the bismuth/boron ratio, showing that boron structural units are relatively stable on the entire investigated composition range.